Once it is jacked up, I use jackstands for security. It isn't a case of "if" the hydraulic jacks goes down, it is a case of "when" it goes down, usually not quickly, but sooner or later a hydraulic jack is going to loose pressure and come down.

IIRC that is one of the strong arguments about the underlying cause that led to the crash of an American Airlines DC-10 back in 1979, which killed everyone on board. Mechanics had supported the engine and pylon assembly with a forklift and left it that way overnight, and the hydraulics in the forklift let it drop a bit, leading to a fatigue crack on the mounting point that ultimately caused the engine separation from the wing.

What with all the 'engineer' types floating around here (I'm a retail kinda guy, myself), what's actually wrong with the #1 photo in this series? I mean, at first glance, it seems pretty sketchy but when you study where everything is placed and look at the additional bracing, it seems safer than the big pile o' pickup sticks that it originally appears to be. I'd climb that rig to get the job done. Can someone explain why I might be wrong?

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Okay, seriously... how drunk do you have to be before this starts looking like a good idea?

Don't know if it'd help but the jack spots are relatively the same on the W211. Although I used the MB tire change jack then put the jackstands on the corners behind the wheels.

The entire front can be jacked up with a hydraulic, just make sure to use jackstands on both sides. I don't know where to jack up the the rear though (again I used the MB jack to bring up one side at a time)

What with all the 'engineer' types floating around here (I'm a retail kinda guy, myself), what's actually wrong with the #1 photo in this series? I mean, at first glance, it seems pretty sketchy but when you study where everything is placed and look at the additional bracing, it seems safer than the big pile o' pickup sticks that it originally appears to be. I'd climb that rig to get the job done. Can someone explain why I might be wrong?

Quality of lumber and bracing aside -ladders are not designated to work as cantilevers. The last 12 feet of that construction is straight cantilever with no other support. Making it several floor levels above the ground sure is not adding safety.

Wood BTW is not giving much warning before it collapses. I do lot of crazy moves in my mechanical and construction activity, but worse come to worse, I would make a safety rope over the light construction. There is guy standing on the ground anyway, so no issues with having safety support.
Saying that I still have all my fingers attached and never had a broken bone (beside cracked ribs).
Lot of my coworkers were not so fortunate.